A few moments later we had crossed the court and had descended into the octagon room of the Tower of Charles the Bold. It was empty. The lamp was burning on the work table, but there was no sign of Old Bob.
“Oh!” cried Rouletabille. He picked up the lamp and carried it from place to place examining everything around him. He tried in turn the lock of every little window which opened from the walls of the basement. Nothing had changed its place, and all was arranged in order and scientific etiquette. While we were looking around at the bones and shells and horns of the prehistoric ages, the “hanging crystals,” the rings made out of bone, the buckles formed from teeth, and the other treasures of the savant, we came to the little desk-table. There we found the “oldest skull in the history of humanity”; and it was true that it had been spattered with the red paint of the wash drawing which M. Darzac had set to dry upon that part of the desk which faced the window and was exposed to the sun. I went from one window to the other and shook the iron bars in order to assure myself that they had not been touched nor tampered with in any way. Rouletabille saw what I was doing and said:
“What are you about? Before thinking about how he could have gotten out at the windows, wouldn’t it be better to find out whether he went by the door?”
He set the lamp upon the parapet and looked for traces of footprints. Then Rouletabille said:
“Go and knock at the door of the Square Tower and ask Bernier whether Old Bob has come in. Ask Mattoni at the postern and Pere Jacques at the iron gate. Go, Sainclair—quick!”
Five minutes after I went out I was back with the information. No one had seen Old Bob in any part of the fortress. He had not passed by anywhere. Rouletabille had his face close to the parapet. He said:
“He left this lamp burning in order to make people believe that he was at work.” And then he added, softly: “There is no sign of a struggle of any sort and in the sand I find the traces of the footprints of only M. Arthur Rance and M. Robert Darzac, who came to this room during the storm last night and have brought on their feet a little earth from the court of the Bold and also of the claylike soil of the outer court. There is no footprint which could be Old Bob’s. Old Bob reached here before and, perhaps, went out while the tempest was raging, but, in any case, he has not come in since.” Rouletabille stood erect. He replaced upon the desk the lamp the rays of which fell directly upon the skull which had been splashed by the red paint in a frightful fashion. Around us there were dozens of skeletons but certainly their presence was less alarming to me than the absence of Old Bob.
Rouletabille stood for a moment staring at the crimson skull, then he took it in his hands and held his eyes close to its empty orbits. Then he raised the skull higher and held it at arms’ length, gazing at it with an almost breathless interest; he looked at the profile. Then he placed the hideous object in my hands and told me to raise it to the level of my head, as carefully as thought it were the most precious of burdens while Rouletabille brought the lamp very close to it.
Like a flash an idea pierced through my brain. I let the skull fall on the desk and rushed through the court till I came to the oubliette. I discovered that the iron bars which closed it were still fast. If anyone had fled by that way or had fallen into the shaft or had thrown himself down, the bars would have been opened. I hurried back, more anxious than ever.
“Rouletabille! Rouletabille! There is no way that Old Bob could have gotten out except in the sack!”